ET confirms that "American Idol" winner David Cook's brother Adam has passed away after a long battle with brain cancer.

Cook announced the sad news Sunday at the Race for Hope fundraising event in Washington D.C. held to fight brain tumors. He said he had lost his brother the previous day, but was still proud to attend the event.

The singer had often spoken of his admiration and inspiration for Adam, including during the "American Idol" competition.

Race for Hope DC has raised more than $7.3 million to find a cure for brain tumors and provide support to brain tumor patients and their families.

After a long and valiant struggle with brain cancer, "American Idol" winner David Cook's brother Adam died at 1 a.m. Sunday morning at a hospice in Terre Haute, IN.

A family friend told RadarOnline.com exclusively, "Adam passed away peacefully. He was surrounded by his family, including his wife Kendra, his children, his father and his step-mom, among others."

David was at the airport Saturday night about to leave for Terre Haute to visit his dying brother, but his family told David they thought it was more important for him to honor a prior commitment to attend the 12th annual Race For Hope in Washington, D.C. Sunday morning.

David followed his family's wishes and went to Washington instead to participate in the race, so he was not there when his brother passed away.

Because David had known how sick his brother was, he had left his tour a few weeks back to say his goodbyes to his older brother.

"The family thought that Adam would go much sooner than this, actually," said the Cook family friend.

"That's why David left his tour a few weeks back so that he could be with Adam. They said their goodbyes then."

But Adam, 36, rallied briefly after that and David returned to his concert tour.

"He took a turn for the worse this weekend" says the friend.

Last year, friends of the stricken lawyer, arranged a $45,000 trip on a chartered medical jet to Los Angeles so Adam could see David perform on Idol.

American Idol winner David Cook choked back tears Sunday morning as he revealed that his beloved older brother Adam had died of brain cancer at the age of 36.

Cook made the announcement during a heartfelt speech at the 12th annual Race For Hope event in Washington, D.C., an event that raises money for brain cancer research.

When Cook was first introduced, the crowd -- not knowing his brother had passed away -- greeted the singer with cheers and applause. Cook even began his speech by making a joke about coming to the race to get a tan , but then a couple of minutes into his talk, the crowd gasped when Cook revealed his brother had just died.

ty will for posting this thread i saw it on one of the idole threads on the idls sight. i am doing to come bk and watch the vid u posted. david showed a lot of love and him and his brother a lot of courage, i am so proud of davis whole family they r so closes and so strong..

Sunday morning, American Idol winner David Cook was still reeling from the death of his older brother Adam, but he didn't let his personal tragedy stop him from serving as grand marshal of Washington, D.C.'s 12 annual Race for Hope 5K.

"David is beyond the most courageous young person I have ever known," says Jeff Kolodin, co-chair of the race, which benefited the National Brain Tumor Society and Accelerate Brain Cancer Cure.

Cook, 26, stood before the 9,000 participants on the rainy Sunday, first joking that he was there to get a tan, then rallying them around the cause before revealing the news of Adam Cook's death.

"I actually lost my brother yesterday to a brain tumor," he told the crowd, choking up over his words, "and I couldn't imagine being anywhere else right now." Adam Cook, 37, a lawyer in Terre Haute, Ind., who was married with kids, had been battling cancer for more than a decade.

In the day's leading up to Adam's death, Kolodin had worked closely with Cook on the race. Cook's team was the top fund-raiser, bringing in more than $98,000, while the race in total raised about $2 million.

"What he did this morning when he was dealing with the most raw emotion was incredible," says Kolodin. "He talked to 9,000 people in a pouring rainstorm today. No one knew his brother had died, but he publicly said to everyone at the race, 'I do have some bad news.' The crowd went pretty much silent and people were crying."

After the grim announcement, Cook put on a brave face, says Kolodin. "He spent his entire day hugging survivors, signing autographs for them, taking pictures. He did this for hundreds of people in a very chaotic setting. "He shared his very private moment with thousands," Kolodin continues. "He was willing to put his personal, raw emotion out there, knowing he was being filmed. He's a heck of a person."

In the American Idol world, the death of current champ David Cook's brother Adam was felt immediately.

Paula Abdul expressed her sympathy in an exclusive statement to PEOPLE: "Adam Cook was a part of our extended American Idol family who supported his brother wholeheartedly, even through his own fight. My heart goes out not only to David, but his family as well."

Adam Cook, 37, had battled cancer for more than a decade, including throughout Cook's bid for the American Idol crown last year. The Terre Haute, Ind., lawyer had even flown out to L.A. amid chemotherapy treatment to see his brother, 26, take the Idol stage.

It was a commitment that didn't go unnoticed by the judges. Simon Cowell, too, offered his condolences. "I was incredibly saddened to hear the news," he said in a statement to PEOPLE. "I met Adam Cook a few times at American Idol. He was an incredible guy, and right now my thoughts are with David and his family."

David posted this blog on his myspace (it brought me to tears again and it was an inspirational blog)

ON BEHALF OF MY FAMILY AND MYSELF

I wanted to write everyone and say a few things, in light of recent events, to dispel any misinformation that may be circulating and to say thank you on behalf of my family and myself to everyone who has shown even the slightest bit of support to us and our efforts as a family to help eradicate this terrible affliction.

My brother, Adam, passed away at 11:52pm Eastern, May 2nd. He was 37 years old and leaves behind his wife and two children. We had played Sunfest in West Palm Beach that night, walking off stage at approximately 11:00pm Eastern, and I rushed to get on a plane to fly to Washington D.C., to be a part of the Race For Hope-D.C., a fundraiser for research and development of a cure for brain cancer. I learned of Adam’s passing upon getting to my hotel around 3:00am Eastern. I decided to run in the race, despite all of this, for two reasons. First, my brother never wanted his illness to affect others. That was evident in the fact that he wanted his illness to have no part in my experience on Idol, a point he was quite adamant about. So, with that wish in mind, I ran and was involved with the event as an homage to him. Secondly, there are many people who are still battling, and by running and sharing my brother’s story, I hope that it offers those still fighting that much more resolve to not succumb to this wretched disease.

I want to again thank everyone who donated to the race and continues to donate, sent a kind email, posted thoughts and prayers, called, etc. I take it as affirmation that my brother was the great man that I knew, and whose ideals I constantly try to uphold in myself. It is with those ideals in tow that I vow to continue to speak out in hopes of raising whatever necessary to help eliminate cancer entirely.

Also, I mentioned earlier that Adam never wanted his illness to affect anyone. So, with the exception of our Toledo, OH, show on May 6th, which we will do everything possible to reschedule, all other shows will go on as scheduled.

Lastly, thank you to everyone for allowing us, as a family, to grieve and come to terms privately. This event has shown me, beyond doubt, that I have the greatest people in my life, family, friends, and fans alike, and for that, I can never offer enough thanks.

"American Idol" winner David Cook took the concert stage Friday night in Ohio, and he alluded several times to his sadness over the loss of his older brother Adam, who passed away from cancer on May 2.

David, brandishing a guitar with his brother's initials on it, sang a little bit of the Eagles' "Hotel California" and told the crowd, "Adam would be proud," says People.com.

Also during the concert, he stopped playing a song and told the audience, "It's gonna be tough for me," adding, "Hold on. I'm sorry. Do you mind if I sing a different song?"

The Web site says that although the 26-year-old star appeared to grapple with his emotions, he at times seemed upbeat, referring to himself as "Old Dave."

David Cook started singing a slow song, stopped and turned away from the audience.

"It's gonna be tough for me," the Idol champ told the crowd of 450 at the Musica theater in Akron, Ohio, on Friday night. "Hold on. I'm sorry. Do you mind if I sing a different song?"

Taking the beat up a notch, Cook then energized the crowd, who passed up flowers and cards and held up signs in honor of his brother, Adam, who died May 2 at age 37 of cancer.

It was a night of emotional extremes for Cook, 26, now back on tour after Adam's death. Speaking of his brother throughout the night, he struggled through some songs – even walking out in the middle of one of them – but exhibited swagger on others.

A Long Road

"It has been a long road for David, and we've seen how tough it has been on him," singer Ryan Star, who has toured with Cook since Feb. 14, tells PEOPLE. " I think he's doing the best he can."

The show opened with Cook walking on stage and singing "Heroes," then raising his guitar to show fans the large black initials "AC" on the front.

At other points, Cook was cheerful, teasing fans and calling himself, "Old Dave" as he chewed gum. But when he covered Fleetwood Mac's "Tell Me Lies," he became emotional at the line, "If I could turn the page."

Then he abruptly left the stage while singing "Come Back to Me," and his band followed. The crowd chanted for his return as he stood in a hallway with his hand to his face, talking to his fellow band members.

A drummer came out and played a solo, and Cook returned in about five minutes, telling the crowd, "It's been a hell of a week. It's good to be here tonight."

ty will for the up date on how david is doing..when i lost my mom not quite 2 yrs ago the hardest thing to do was keep it together i stayed in the house because this wave of sad ness would come over me and i never new when it would hit and i would burtst into tears. i couple of time i had to run to my car or hide in the grosery stor on a deserted isle.. i just relised that last mothersday i cryed all day i am not crying i must be getting stronger thank u lord..